While the mechanism behind the association is unknown, a new study finds that depression after being diagnosed with coronary artery disease doubles the risk of mortality.

A new study has examined the risk of premature death in patients having been diagnosed with both depression and coronary artery disease.Coronary artery disease (CAD) is the most widespread form of heart disease. And recently, more and more studies have been pointing to the effect of psychological distress or depression on the risk of mortality among patients with CAD.

Now, a team of researchers at Intermountain Medical Center Heart Institute in Salt Lake City, UT, United States (US), have conducted a large-scale study to investigate the link between being diagnosed with CAD and afterward receiving a diagnosis of depression.

The team was led by Dr. Heidi May, a cardiovascular epidemiologist at Intermountain Medical Center Heart Institute, and the findings were published in the European Heart Journal: Quality of Care & Clinical Outcomes.

May and team examined a total of 24,137 patients with CAD, as diagnosed by an angiography. Using the International Classification of Diseases codes – a standard diagnostic tool – the researchers determined whether or not the patients had depression.

They then used Cox hazard regression models to adjust for the different periods of time that had elapsed between being diagnosed with CAD and being diagnosed with depression. These lengths of time differed from patient to patient.

Overall, 3,646 (15 percent) of the patients received a diagnosis of depression during CAD follow-up. These patients tended to be younger and female, compared with their depression-free counterparts. They were also more likely to have diabetes and to have been previously diagnosed with depression.

Additionally, they were less likely to develop a myocardial infarction, or heart attack, during follow-up.Of all the patients diagnosed with depression, 27 percent received their diagnosis within a year of the CAD diagnosis, 24 percent within one to three years after the heart disease diagnosis, almost 15 percent between three and five years, and almost 37 percent more than five years after the heart event occurred.

Having adjusted for all of these factors, the researchers found that “post-CAD depression was the strongest predictor of death.”In fact, being diagnosed with depression at any point after receiving a CAD diagnosis raised the risk of dying prematurely by twofold.Even among patients who had no history of depression diagnosis, this correlation was just as strong.